Evaluation of technologies for purification of greenhouse horticultural discharge water

The demands of the European Water Framework Directive for ecological and chemical good water quality, resulted in the need for the greenhouse horticultural sector to decrease the emission of nutrients and plant protection products (PPP) drastically in the coming years. To reach this goal, our research follows a dual approach by 1) developing techniques and methods for further recirculation of nutrient solutions, and 2) end-of-pipe solutions for emission via discharge of the nutrient solutions. Here we present our research on an end-of-pipe solution for PPPs, which is the use of water purification techniques. The technologies are tested on effectiveness of removing PPPs from so-called ‘Standardised Water’, which contains specified amounts of nutrients, dissolved organic matter and twelve active ingredients of PPPs. Also applicability in a greenhouse environment and economic feasibility are examined. Four technologies were chosen to be investigated: 1) Ozone with and without activated carbon, 2) Hydrogen peroxide (H2O2) with middle pressure UV-radiation, 3) H2O2 with low pressure UV-radiation, and 4) Electrochemical flocculation. Ozone and H2O2 – UV (both low and middle pressure) proved to be able to remove the PPPs with an effectiveness of approximately 80%. Activated carbon filter after ozone treatment improved effectiveness up to 100% (short run). Electrochemical flocculation showed an effectiveness of around 40%, but it should be noted that a suboptimal pilot device was tested. Cost calculations of the three most promising technologies were carried out using four case studies. The calculations showed that ozone treatment has the highest cost per m3 of treated water, followed by H2O2 with middle pressure and low pressure UV treatment. In general, the applicability of the three technologies (ECF excluded) in greenhouse horticulture was assessed as good.